Statistical multiplexing at optical level provides a theoretical gain in terms of transmission resources exploitation respect to traditional circuit based WDM rings. However its performance is strongly affected by the mechanisms adopted for bandwidth allocation in real time to the different services at both node and network levels. Typically the bandwidth assigned to guaranteed traffic is pre and over provisioned causing a relevant waste of optical resources. For the best effort quote of the traffic typically the queues status in the nodes is used to allocate the optical bandwidth. Fast methods, like “one-way reservation”, cause collisions and consequent retransmission, while collisionless techniques, like “two way reservation”, take milliseconds to take a decision and are generally processing consuming. Both approaches can lead to relevant delays, put restrictive constraints on wavelengths use in the ring and can be unfair in resources allocation, providing efficiency slightly better if compared to circuit based WDM rings. As a consequence, nowadays optical statistical multiplexing is difficult to apply in telecom-grade networks and for cloud computing applications that are the emerging fields for this technology.
Ring networks are a primary choice for fiber-based metropolitan area networks (MAN), because they minimize fiber deployment costs, and simplify routing, control, and management issues. In the last years, new applications and services, such as video on demand (VoD), video broadcasting, and IP telephony, are significantly changing MAN traffic characteristics, in terms of both required bandwidth and quality of service (QoS) assurance. In the future, video-related traffic will exceed best effort traffic in terms of required bandwidth, hence the interest of many network operators to effectively accommodate QoS traffic in their MANs. This means providing different latency and priority characteristics to the different classes of service supported.
Optical burst switching is an alternative to traditional circuit based WDM networks. It can allow a better exploitation of bandwidth resources (up to 70% if compared to circuit solutions), introducing statistical multiplexing at optical level. However, this technology needs efficient real-time dynamic bandwidth allocation mechanisms at both node and network level to both maximize bandwidth exploitation and keep QoS constraints satisfied.
Performance of optical burst switching solutions are strongly affected by the mechanisms adopted for bandwidth allocation in real time to the different services at both node and network level. Several bandwidth allocation schemes are available in existing literature. Bandwidth allocation relies on two main mechanisms: Connection Admission Control (CAC) and the Media Access Control (MAC). The first determines the effective bandwidth needed at network level by each service to satisfy its QoS. The second controls the runtime bandwidth allocation at node level in coordination with the other nodes in the network in order to satisfy services' demands as they change from time to time. Literature and products refer to a series of methods trying to support bandwidth allocation in the most efficient way. CAC is typically not treated or is primitive (e.g. bandwidth assigned to a connection in a pre-provisioned way guessing the needed guaranteed bandwidth). MAC consists of a control part located in the nodes, handling the local scheduling of traffic according to a specified policy, and a protocol part used to exchange information among the nodes to allow nodes decision when to transmit into the ring. The transmission of the control information is typically out of band, using an extra wavelength.
Among the various known MAC control strategies some examples are as follows:                CSMA/CA Carrier sense multiple access with collision avoidance.        Wavelength availability information on control channel.        Two way reservation technique.        Pre-provisioning and exchange of information on excess available BW with CA.        
Such techniques mean that CAC is usually not defined and a guessed guaranteed bandwidth is reserved. Depending on the MAC mechanism adopted, there can be data losses triggering retransmissions, or if lossless, they introduce a significant delay on traffic equal to the RTT of the ring (typically 1 or more milliseconds).